September 28, 2022

The ethics of marrying cousins

The risk is small that previously believed.

Is it unethical to marry your cousin?
Obviously the answer must depend on the risk of birth defects amongst
your children. And according to a New Zealand scientist Hamish
Spencer, writing in PloS Biology, the risk is not very high. In 2002
an expert panel convened by the National Society of Genetic
Counselors (in the US) found that the risks of a first-cousin
marriage are about 1.7% to 2% above the background risk for
congenital defects and 4.4% above the background for dying in

Spencer concludes that “neither the
scientific nor social assumptions behind [anti-cousin-marriage laws]
stand up to close scrutiny. Women over the age
of 40 have a similar risk of having children with birth defects and
no one is suggesting they should be prevented from reproducing.
People with Huntington’s disease or other autosomal dominant
disorders have a 50 per cent risk of transmitting the underlying
genes to offspring and they are not barred either.”

However, in 31
American states, cousin marriage is banned or permit it only where
the couple obtains genetic counseling, is beyond reproductive age, or
if one partner is sterile.

This study has political implications,
as people from Middle Eastern backgrounds tend to marry cousins. As
many as 50% of all marriages in Turkey and Morocco, for instance, are
between first and second cousins. When communities from these
countries migrate, they bring their customs with them, much to the
consternation of politicians.

The authors of the paper call for the
abolition of cousin marriage laws in the US: “These laws reflect
once-prevailing prejudices about immigrants and the rural poor and
oversimplified views of heredity, and they are inconsistent with our
acceptance of reproductive behaviors that are much riskier to
offspring. They should be repealed, not because their intent was
eugenic, but because neither the scientific nor social assumptions
that informed them are any longer defensible.” ~ Newsweek,
Dec 30;
Biology, Dec 23